TCL/OTCL

Common NS classes

The following figure shows the most commonly used NS classes in writing a network simulation:

Notes:

A node simulates a router (Network Level object).

A node object implements the complete IP protocol layer
The node object contains program code that compute minimum cost routes from any node to any other node
(You don't need to worry about routing or re-routing)

Transport level "agents":

Agent/TCP is the TCP Tahoe sender
Agent/TCP/Reno is the TCP Reno sender
Agent/TCP/Sink is the TCP Reno receiver (sends back ACK messages to the sender)
Agent/UDP is the UDP sender
Agent/NULL is the UDP receiver (it de-allocate the IP packets)

Each Transport level agent must be associated with a node (= Network level agent)

Traffic generators:
Each Traffic generator must be associated with the corresponding type of Transport level agent

Steps in writing a network simulation in NS2

Recipe for writing a network simulation program in NS2:

Create a Simulator object

Example:

set ns [ new Simulator ]

Create the network:

Create nodes (routers): click here

Example:

set n1 [ $ns node ] set n2 [ $ns node ]

Connect the nodes with (duplex) links: click here

Example:

$ns duplex-link $n0 $n1 10Mb 10ms DropTail

Create TCP source and TCP sink

set tcp1 [new Agent/TCP/Reno] set sink1 [new Agent/TCPSink]

Associate (attach) the TCP agents to a node (Network layer):

$ns attach-agent $n0 $tcp1 $ns attach-agent $n1 $sink1

Connect a TCP source to a TCP sink

$ns connect $tcp1 $sink1

(This will make a TCP connection !!!)

Create a traffic generator for the TCP source:

set ftp1 [new Application/FTP]

Associate (attach) the traffic generator to a TCP source agent:

$ftp1 attach-agent $tcp1

And we are ready to rip !!!

I have more detailed notes below that clarifies each step